Deep drawing steels and method of making the same



Patented- Sept. 12, 1944. I

I DEEP DRAWING STEELS AND DIETHOD OF MAKING THE SAME VValter Crafts'and Cecil G. Chadwick, Niagara. Falls, N. Y., assignors to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application December 1, 1942,

Serial N0. 467,553

6 Claims. (01. 75-123) The invention relates to deep drawing steels, to deep drawn articles made therefrom and to a method for preparing deep drawn steel.

Deep drawing steels of the low carbon, aluminum-killed type are currently employed in large quantity by industry. Silicon-killed steels are, in' general, less satisfactory due to the hardening effect of the silicon addition.

It is the primary object of the present invention to provide a silicon-killed steel having good deep drawing properties. Another object is to provide deep drawn articles having smooth surface characteristics. A further object is to provide a silicon-killed deep drawing steel of uniform grain size, the properties of which are comparable to plain, aluminum-killed deep drawing steels. A' still further object is to provide a method of preparin deep drawn steel of siliconkilled steel.

These and other objects are achieved by the invention which is based on the discovery that boron'exerts a softening effect in low-carbon deep drawing steels and that this effect may be utilized to compensate for the hardening effect of silicon. By substituting silicon for the normal or part of the normal aluminum addition in lowcarbon deep drawing steels and additionally treating such steels with boron, properties comparable to those of aluminum-killed deep drawing steels may be obtained.

The invention in its broader aspect comprises deep drawing steels or articles made therefrom containing between 0.01% and 0.10% carbon, 0.10% to 1% manganese, 0.05% to 0.50% silicon, 0.0005% to .05% boron, remainder iron and incidental impurities such as normally occur in the manufacture of low carbon steels of good quality. In a preferred embodiment of the invention, the upper limit of manganese below 0.50%,

the upper limit of silicon below 0.30% and the boron between 0.001% and 0.02%. Although steels containing silicon in rather large amounts may be benefited by treatment with boron, it nevertheless appears advisable to limit the siliconaddition to the lowest amount consistent with good deoxidation practice.

In accordance with the present invention, deep drawn articles may be made by preparing a low carbon steel: melt containing carbon in an amount less than 0.10%, treating the melt with silicon in any desired form, as for example, ferrosilicon, in an amount sufficient to deoxidize the melt but insuflicient to leave a residual silicon content greater than 0.50%. preferably no greater than 0.30%, adding boron in an amount 'priate relative proportions.

sufficient to counteract the hardening effect of the silicon addition, the boron addition being between 0.0005% and 0.05%. preferably between 0.001% and 0.02%, casting the resulting steel melt and rolling the same to sheet and thereafter subjecting to a pressing operation-to form a deep drawn article.

The boron addition may be made in almost any convenient form. For example, it may be added as an oxide or a salt, such as borax; as a. boride or other compound, such as boron carbide; as a metallic alloy, such as manganese-boron or calcium-boron; or it may be added in combination with silicon in the form of a ferrosilicon-boron alloy or in combination with manganese and silicon in the form of an iron-manganese-silicon-boron. Although the invention is not limited to the use of any specific agent for adding boron, and the types of agents just mentioned aremerely suggestive of the wide range of possible means by which the boron addition may be made to the steel, nevertheless under some conditions particularly favorable results are obtainable by the use of an agent consisting essentially of silicon, manganese, boron and iron in appro- Preferred proportions comprise 20% to silicon, 60% to 20% manganese, 1% to 15% boron, remainder iron and other incidental impurities.

Due to the existence of many external factors which enter into deep drawing operations, there is no single standard test which can be directly interpreted in terms of commercial deep drawing properties. Among the variables encountered in the deep drawing of steel are the type of lubricant employed, the die construction, the rate of draw, and the surface finish required on the final deep drawn article. There are, however, certain physical properties, determinable by simple testing, which are accepted as indicia of the relative deep drawing characteristics of steels. In general, these properties are low yield point, moderately low tensile strength and hardness, good elongation as measured by percentage elongation in tensile test, depth of cup in cupping test, and substantial freedom from aging effects.

The excellent properties obtained by utilizing silicon as a deoxidizing agent and additionally treating the silicon-killed steels with boron is shown in Tables A and B in which Table A sets forth the compositions of the steels and Table B the physical properties. The steels of the series were all deoxidized in the furnace, cross-rolled to form sheets 0.05 inch in thickness, sandblasted and pack annealed. After annealing, the sheets were pickled and cold-rolled to 0.04 inch in thickness. The cold-rolled sheets were then annealed at the temperatures indicated in Table ed with a boron addition according to the invention. The softening effect of the boron addition to the silicon-killed steels may be seen by a comparison of Steels Nos. 3, 4 and 5 with the plain B, pickled, and finally given a cold roll pinch 5 silicon-killed Steel No.2. This comparison shows pass equivalent to two per cent reduction. One that the boron additions have effected a lowerset of specimens was tested after the foregoing ing of-the yield point, tensile strength and hardtreatment. A corresponding set of annealed 'ness and have increased the ductility as measured specimens was tested after the foregoing treatby the percentage elongation and Erichsen values ment plus an accelerated aging treatment that while maintaining a uniform grain size. comprised heating the specimens at 200 C. for As indicated by these data, silicon when added 24 hours in an air atmosphere. A visible oxide alone for purposes of deoxidation, hardens and formed on the specimens due to the aging treatstrengthens the steels, and also lowers their ducment, which oxide was not removed prior to testtility to an undesirable degree. Additional treats t specimens- 16 ment of the silicon-killed steels with a small In Table B, Y. P. means yield point in amount of boron as contemplated by the present pounds per square inch; T. S. means tensile invention compensates for these undesirable efstrength in pounds per square inch; E1 fects of silicon and enables the production of means percentage elongation in a gauge length silicon-killed steels of excellent deep drawing of two inches; Hardness RB means the hard- 20 characteristics. ness value on the Rockwell B scale; Erich- While specific examples have been given in the sen means the greatest depth of indentation foregoing specification, these examples are given measured in millimeters made in the Erichsen merely to illustrate the principles of the invencupping test before incipient crackin of the tion and the invention is not limited to or by such sheet; and "A. S. T. M. grain size" means the examples. actual grain size as measured according to the We claim: American Society for Testing Materials grain 1. Deep drawing silicon-killed steel containing size index. between 0.01% and 0.1% carbon, 0.10% to 1% TABLE A manganese, 0.05% to 0.50% silicon, 0.0005% to 0.05% boron, remainder iron and incidental imcomposition of steels by chemical analysis purities; and said steel being substantially free mai d substantially iron) from deoxidizing elements, and deoxidation products thereof, other than said manganese, silicon, Steel NO. Per cent Per cent Per cent Per cent Percent and boron- 0 Mn s1 Al 13 1 2. Deep drawing silicon-killed steel contammg 0.04% to 0.07% carbon, 0.10% to 0.50% man- 8-8? 3% 3-02 n ganese, 0.10% to 0.30% silicon, 0.001% to 0.0 3111111111111 004 0150 0105 ZIIIIIIII "0'61 r remainder ir and incidental impuri- 8-8; 8-23. 8' 8% ties, said boron addition serving to counteract 40 the hardness imparted by the silicon addition; ,Nominal analysis and said steel being substantially free from de- Added amount. oxidizing elements, and deoxidation products TABLE B Physical properties steel Heat treatment altercold rolling Y. P. T.S Percent 1 122? Eriehsen A S-'T'-M N o. El RB grain size Annealed (1) 23,850 44, 750 as 39 11.7 5 Annealed (1) and aged 33, 750 45,650 34 47 11.4 1111110010 (1) 32, 550 53,450 20 53 11.1 5 Annealed 51) and aged 37,800 51,700 28 10.8 Anne 0 2) 23,750 42,500 35 as 11.5 5 Annealed (2) and aged 32,200 42,750 40 40 11.7 Annealed 1 27,500 48,050 as 44 11.5 5 Annealed (l) and aged 35, 650 ,950 33 50 11.0 Annealed (2) 27,850 47,950 36 34 11.4 -6 5 Annealed (2) and aged 36,050 33 43 11.4

Annealed (l)=925 O.furnaoe cool to 710 0., 8 hours-furnace cool.

Annealed (2)fl25 C.air cool, 710 C., 8 hoursiurnace cool.

Aged=200 C.24 hours-air cool.

In the tables, Steel No. 1 is a low carbon aluminum-killed steel of typical physical properties, such as currently employed in industry for deep drawing purposes. Steel No. 21s a plain low carbon steel in which silicon was employed as the deoxidizingagent for killing the steel. It will be noted that the yield point of the silicon-killed steel (No. 2) is considerably higher than that of the aluminum-killed steel (N0. 1) and further that the silicon-killed steel is harder, has less elongation, and less cupping depth than the aluminum-killed steel. This condition exists in both the annealed and in the annealed and aged state. Steels Nos. 3, 4 and 5 are silicon-killed steels of increasing silicon content which have been treatthereof, other than said manganese, silicon, and boron.

3. An article, deep drawn to requisite shape, and composed of a silicon-killed steel containing between 0.01% and 0. carbon, 0.10% to 1% manganese, 0.05% to 0.50% silicon, 0.001% to 0.05% boron, remainder iron and incidental impurities, said steel being characterized in that it has enhanced deep drawing characteristics over a silicon-killed steel of similar composition containing no boron; and said steel being substantially free from deoxidizing elements, and deoxidation products thereof, other than said manganese, silicon, and boron.

4. An article, deep drawn to requisite shape,

and composed of a silicon-killed steel containing 0.04% to 0.07% carbon, 0.10% to 0.50% manganese, 0.10% to 0.30% silicon, 0.001% to 0.02% boron, remainder iron and incidental impurities, said steel being characterized in that it has enhanced deep drawing characteristics over a silicon-killed steel of similar composition containing no boron; and said steel being substantially free from deoxidizing elements, and deoxidation products thereof, other than said manganese, silicon, i0

and boron.

5. A method of preparing deep drawing steel comprising preparing a melt of low carbon steel containing carbon in an amount less than 0.10%

CECIL G. CHADWICK. 

